Resistance coupled amplifiers



May 2, 1933. B. VAN DER POL Err A1. 1,907,225

RESISTANCE COUPLED AMPLIFIERS Filed Jan. 24, 1950 M ff INVENTORS BALTHASAR VAN DER POL AfToRNEY AND JAN AN ER MARK Patented May 2, 1933 j i UNITED STATES BALTHAsA-R VAN DER Poi. AND

JAN VAN DER MARK, 0F EINDHOVEN, NETHERLANDS,

Y'ASVSIGNORS TQ RADIO CORPORATION, 0F AMERICA, A CORPORATION 0F DELA- wenn The present invention relates to amplifiers, and more particularly to improvements in, or relating to, low frequency resistance Coupled amplifiers. y

With low frequency amplifiers ofthe resistance coupled type it may occur that, due

to parasiticcapacities or slight self-induc' tances inthe coupling resistances and in the connectingleads or in the sources of voltage, the amplification is not perfectly uniform for the whole range of frequencies to be amplified. Even if the utmost care is bestowed on the construction, it is not always possible to eliminate this non-uniformity. In many cases, however, it is desirable to obtain a perfectly uniform amplification of the whole low frequency range. The invention has, then, for its main object the provision of a means for achieving this result.

Another important object of the invention is to provide an amplifier so constructed that the anode circuits of at least two valves, whose ordinal numbers in the cascade connection differ by an odd number, comprise a common resistance or impedance.

Still another object of the invention is to provide an amplifier circuit arrangement comprising an even number of amplification stages, all the anode circuits in which have a common portion.

The novel features which we believe to be characteristic of our invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which we have indicated diagrammatically several circuit organizations whereby our invention may be carried into effect.

The invention will be set forth more fully with reference to the accompanying drawing which represents, by way of example, two embodiments of the invention.

In the drawing,

Fig. 1 diagrammatically shows a fourstage amplifier in which the anode circuits of the first and last thermionic devices comprise a common impedance,

RESISTANCE COPLED AMPLIFIERS Y, Application lefi January 24, 1930, serial no. 423,006, and in the netherlands February 15, 1929.

Fig. 2 shows a modified form of circuit in which alll the anode circuits comprise a common impedance. i

Referring to Fig. 1the thermionic devices are denotedby 1, 2, 3 and 4, and the coupling condensers by, Gand 7. The filaments and anodes of the tubes are energized by current sources 8 and 9 respectively. The elements 10, V11, 12 and 13'denote the coupling resistances or impedances. Theresistances 11 and 12 are directly connected by the'lead 15 to the positive pole of the anode current source 9, whereas the resistances 10 and 13 are both connected to the said pole through a resistance or impedance 14. Y

Fig.'2 diers from Fig. 1 only in that the resistances orimpedances ,11 and 12, instead of being directly connected to the positive terminal of the anode battery areconnected thereto through the impedance'14. It has been found that the use of this common 'impdance results ina perfectly uniform amplilication of a very broadrange of frequencies.

The impedance 14C need not have -a high value.l In a four-stage amplifier of actual construction, resistance 141 was given a value Vof 1000 ohms, whereas the resistances 10, l1, 12 and 13 had values' of about 200,000 ohms. After the resistance 14 had been provided the characteristic, which without impedance 14 showed great irregularities, was found to be almost perfectly jstraight up to about 15,000 cycles per second. A suitable choice of the impedance 14 results in a more or less powerful amplification, over definite frequency ranges, and to thus alter somewhat the shape of the frequency characteristic. Y

If, for example 14; is a resistance shunted by a'capacity 15', a powerful amplification of the high frequencies is obtained.

While ywe have indicatedy and described several systems for carrying our invention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organizations shown and described, but that many modifications in the circuit arrangements, as well as in the apparatus employed, maybe made without departing 'from' the scope of our invention as set forth in the appendedclaims.

What we claim is:

l. In combination, in a resistance coupled audio frequency amplifier, a plurality of amplifier tubes in cascade, a source of anode potential, a capacitybetween the anode of each preceding tube and the grid of each succeeding tube, a common lead between the positive terminal of said source and each of the tube anodes, a coupling resistor between each anode and the common lead, a common impedance, in series with each coupling resistor, being disposed in said common lead between said couplingV resistors and said positive terminal to secure perfectly uniform audio amplification over the whole range of audio frequencies up to 15,000 cycles, said impedance having a resistive magnitude of the order of one-two hundredth of said coupling resistors.

2. In combination, in an audio frequency amplifier, a plurality of amplifier tubes in cascade, a source of anode potential, a capacity between the anode of each preceding tube and the grid of each succeeding tube, a commonlead between the positive terminal o f said source and each of the tube anodes, a coupling resistor between each anode and the common lead, a common resistor, in series with each coupling resistor, being disposed in said' common lead between said coupling resistors and said positive terminal to secure uniform audio amplification upV to 15,000 cycles, the'magnitude of said common resistor being of the order of one-two hundredth of the magnitude of any of said coupling resistors.

, 3. In combination, in an audio frequency amplifier, a plurality of amplifier tubes in tively connected to the remaining coupling resistors, each of said coupling resistors having a value at least two hundred times greater than said common resistor whereby perfectly uniform amplification of the whole audio frequency range up to substantially 15,000 cycles is secured.

5. In combination, in a resistance coupled audio frequency amplifier having a perfectly uniform amplification characteristic over a broad range of audio frequencies extending up to 15,000 cycles, a plurality of amplifier tubes in cascade, a source of anode potential, a capacity between the anode of each preceding tube and the grid of each succeeding tube, a common lead between the positive terminal ofthe source and the anodes of the first and last tubes, a common lead between said terminal and the anodes of at least two intermediate tubes, a coupling resistor between each anode and its common lead, and a common impedance of a magnitude one-two hundredth of any coupling resistor between the last coupling resistor and said terminal.

BALTnAsAR VAN DER PoL.

J AN VAN DER MARK.

cascade, a source of anode potential, a capacity between the anode of each preceding tube and the grid of each succeeding tube, a common lead between the positive terminal of said source. and each of the tube anodes, a coupling resistor. having a value of the order yof 200,000 ohms between each anode and the common lead, a common impedance having a value about one-two hundredth of said first mentioned value in series with each coupling resistor, being disposed in said common lead between said coupling resistors and said positive terminal to secure uniform audio amplification up to 15,000 cycles, and a capacity in shunt-with said common impedance to accentuate the amplification of the higher audio frequencies.

l 4. In combination, in a resistance coupled audio frequency amplifier, a plurality of amplifier tubes in cascade, a source of anode p-otential, a capacity between the anode of each preceding tube and the grid of each succeedingtube, .a coupling resistor between each anode and the positive terminal of said source, and a common resistor between the last coupling resistor and said positive terminal, said common resistor being conduc- 

